Date: Sat, 4 Oct 2014 11:29:43 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Kohji Okuno <okuno.kohji@jp.panasonic.com> Cc: stable@freebsd.org, freebsd-current@freebsd.org Subject: Re: About pmap_mapdev() & pmap_unmapdev() Message-ID: <20141004082943.GN26076@kib.kiev.ua> In-Reply-To: <20141004.170036.336251378907610162.okuno.kohji@jp.panasonic.com> References: <20141003.172533.863334695746935674.okuno.kohji@jp.panasonic.com> <20141003215830.GK26076@kib.kiev.ua> <20141004.170036.336251378907610162.okuno.kohji@jp.panasonic.com>
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On Sat, Oct 04, 2014 at 05:00:36PM +0900, Kohji Okuno wrote:
> Hi, Konstantin,
>
> Thank you for your comment.
> And, your change is better than mine.
At the end of the mail is commit candidate. I did not even compiled this.
Can you test and report back, please ?
>
> > Do you mean that this panic is related to missed pmap_remove() ?
> > I doubt it, since pmap_mapdev() does not establish managed mappings.
>
> Yes, pmap_mapdev() does not establish managed mappings. But, if
> kernel_pmap.pm_stats.resident_count is zero, then any managed pages
> (for example pipe_map, exec_map, or etc.) are not able to change
> unmanaged status, because pmap_remove() returns without calling
> pmap_remove_pte().
>
> In this result, I encounterd the panic. Could you refer the following?
Yes, kmem_back() indeed uses managed mapping.
Index: amd64/amd64/pmap.c
===================================================================
--- amd64/amd64/pmap.c (revision 272506)
+++ amd64/amd64/pmap.c (working copy)
@@ -5040,6 +5040,9 @@ pmap_mapdev_attr(vm_paddr_t pa, vm_size_t size, in
pa = trunc_page(pa);
for (tmpsize = 0; tmpsize < size; tmpsize += PAGE_SIZE)
pmap_kenter_attr(va + tmpsize, pa + tmpsize, mode);
+ PMAP_LOCK(kernel_pmap);
+ kernel_pmap.pm_stats.resident_count += OFF_TO_IDX(size);
+ PMAP_UNLOCK(kernel_pmap);
pmap_invalidate_range(kernel_pmap, va, va + tmpsize);
pmap_invalidate_cache_range(va, va + tmpsize);
return ((void *)(va + offset));
Index: i386/i386/pmap.c
===================================================================
--- i386/i386/pmap.c (revision 272506)
+++ i386/i386/pmap.c (working copy)
@@ -5066,10 +5066,14 @@ pmap_mapdev_attr(vm_paddr_t pa, vm_size_t size, in
size = roundup(offset + size, PAGE_SIZE);
pa = pa & PG_FRAME;
- if (pa < KERNLOAD && pa + size <= KERNLOAD)
+ if (pa < KERNLOAD && pa + size <= KERNLOAD) {
va = KERNBASE + pa;
- else
+ } else {
va = kmem_alloc_nofault(kernel_map, size);
+ PMAP_LOCK(kernel_pmap);
+ kernel_pmap.pm_stats.resident_count += OFF_TO_IDX(size);
+ PMAP_UNLOCK(kernel_pmap);
+ }
if (!va)
panic("pmap_mapdev: Couldn't alloc kernel virtual memory");
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